Part (but by no means all) of the reason for this was an absence of any sufficiently accurate means of keeping time, i.e. of a reasonably good ‘clock’. Such a clock is needed so that changes in position can be accurately timed, and so that the speeds and accelerations of bodies can be well ascertained. Thus, Galileo’s observation in 1583 that a pendulum could be used as a reliable means of keeping time had a far-reaching importance for him (and for the development of science as a whole!) since the timing of motion could then be made precise.4 Some fifty-five years later, with the publication
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